Samples of martensitic-hardened bearing steel 100Cr6 (AISI 52100) were exposed to hydrogen atmospheres at different gas pressures. The resulting hydrogen contents were measured, and a pressure-dependent hydrogen charging curve was established. Tensile tests on cylindrical specimens charged at various hydrogen pressures showed a pronounced reduction in strength at hydrogen contents as low as 0.75 × 10–6. Fractographic analysis revealed predominantly intergranular fracture with crack propagation along carbide-featured grain boundaries, indicating hydrogen enrichment at microstructural traps. Specimens, in which diffusible hydrogen was allowed to outgas prior to testing, largely recovered their initial strength, demonstrating that the observed embrittlement is mainly governed by diffusible hydrogen and is, to a significant extent, reversible. These findings provide insight into the pressure-dependent influence of hydrogen on the strength and reliability of bearing components operating in hydrogen environments.

Sliding bearings in pumps operating under corrosive and insufficiently lubricated conditions are subjected to high levels of wear and degradation, frequently resulting in accelerated component failure. These bearings typically utilize tungsten carbide with a cobalt binder (WC-Co) due to its superior resistance to wear and corrosion. However, growing concerns regarding the sustainability and limited availability of tungsten and cobalt have intensified the efforts to develop alternative, resource-efficient solutions. To address this challenge, a novel ceramic coating composed of chromium carbide-chromium oxide (Cr3C2/Cr2O3), deposited using high-velocity suspension flame spraying (HVSFS), was evaluated as an environmentally sustainable replacement for WC-Co coatings in sliding bearing applications. Shaft sleeves were coated and subsequently cylindrical grinding was applied to achieve tight dimensional tolerances and optimal surface finish. Ultrashort-pulsed laser surface texturing was then employed to create engineered dimples designed to improve friction behavior under challenging lubrication conditions. A fine cylindrical grinding was subsequently applied to remove residual pile-up and flatten inter-dimple areas. Grinding performance evaluation demonstrated 20% reduction in tangential grinding force and 37% improvement in surface roughness (Rz) compared to WC-Co, confirming the coating's suitability for precision finishing. Tribological tests under water-lubricated sliding conditions revealed that laser-textured Cr3C2/Cr2O3 coatings exhibited up to 50% lower wear mass than non-textured coatings and achieved friction coefficients between 0.02 and 0.04, matching WC-Co performance while showing greater stability and lower variability. In speed-ramped Stribeck testing, laser-textured surfaces maintained reduced friction variability and closely followed the frictional trend of WC-Co, particularly in the boundary-to-mixed lubrication regime. These findings highlight the combined advantages of the proposed coating system in terms of machinability, wear resistance, friction control, and operational consistency, offering a viable and sustainable alternative for high-performance sliding bearing applications in water-lubricated environments.

This publication focuses on the influence of the contact geometry and especially the particle ejection on the tribological behaviour of unlubricated, thermally highly loaded contacts by a systematic comparison of a system and a model test. Moreover, the influence of temperature and the influence of an exhaust gas atmosphere on the tribological system behaviour of an austenitic cast iron was analysed in depth. Between the system and model experiments, the dominant tribological mechanisms are broadly comparable, and the corresponding temperature regimes of the wear behaviour show excellent agreement. However, the wear rates and atmospheric effects are significantly different. By using grooved bushings, the influence of the particle ejection and thus the contact geometry on the tribological behaviour was analysed. For lower temperatures, comparable wear rates and atmospheric influences between the tests are only determined with grooved bushings.

The aim of this research is to present the use and advantages of electro-active eco-fluids as smart biolubricants. Polarizable clay mineral nanoparticles, such as the layered nanosilicate montmorillonite Cloisite 15A and the fiber-like sepiolite Pangel B20, were dispersed in a sustainable fluid, castor oil, at concentrations of 0.5, 2, and 4 wt%. These dispersions exhibit electro-viscous behavior, which was characterized by higher yield stress values with increasing electric field strength. Based on this, the influence of electric potentials was investigated in an electrified axial ball bearing device. The coefficient of friction (COF) was changed as needed and reversibly when different electric fields of 100 and 200 V/mm were applied. A 10.7% increase in the coefficient of friction was observed with a 4 wt% Cloisite 15A in castor oil at 200 V/mm. In the case of Pangel B20, the application of an electric field of 200 V/mm successfully prevented the lubricant from being displaced from the contact zone at 500 r/min. In addition, the dielectric breakdown resistance of these clays was analyzed. Cloisite 15A yielded better results than Pangel B20, probably due to its greater electro-responsive and thus film-forming potential. Finally, the load-carrying capacity was also evaluated. Under the action of an electric field, an opposite vertical force was observed when a ball was pressed onto a plate with a lubricating film in between. Consequently, the study allows conclusions to be drawn about a new lubrication concept based on electro-active control of friction in electrified tribological contacts by fully sustainable electro-rheological (ER) lubricating fluids.

The effectiveness of conductive lubricants, particularly ionic liquids (ILs), in mitigating premature failure such as hydrogen-assisted rolling contact fatigue (HARCF) in rolling-contact bearings is investigated. The degradation of lubricants under tribological load leads to hydrogen generation, contributing to HARCF. The addition of ILs to lubricants significantly enhances their electrical conductivity, thereby preventing premature failure and extending bearing lifespan. Experimental investigations, including linear-oscillation sliding and rolling-contact fatigue tests, confirm the superior performance of a lubricant containing 3.0 vol% Trihexyltetradecylphosphonium-bis (trifluoromethylsulfonyl)-imide [P66614][BTA]. These findings provide valuable insights into enhancing bearing reliability in industrial applications.

This study investigates the influence of temperatures, normal force, displacement, frequency and sliding distance on the tribological material behaviour of an unlubricated cobalt-based material pairing, as well as the effects resulting from a change of atmosphere from ambient air to a low-oxygen CO2/N2/O2-atmosphere. The subsequent identification of empirical wear correlations should enable a transfer to other material systems. Reciprocating wear tests were carried out at up to 800 degrees C with a cylinder-on-plate contact geometry. The test conditions and the material are based on the application as exhaust gas flap plain bearings for combustion engines. The temperature has a major influence on the wear behaviour, as it induces the change of tribological mechanisms from abrasion to oxidation and adhesion of wear particles to the formation of a glaze layer in the HT range. The wear particles, required for the tribologically induced sintering process of the glaze layer, are already present in fully oxidised format low temperatures of 200 degrees C. The formation of a wear-reducing glaze layer is therefore mainly dependent on the temperature, as this directly influences the sintering process, according to a key finding of this work. The atmospheric influence on the tribological material behaviour is dependent on the temperature related wear regime. For lower temperatures, a mechanism change from abrasion to adhesion takes place in the oxygen-reduced CO2/N2/O2-atmosphere. In contrast, the formation of the glaze layer is not influenced by the change in atmosphere. Moreover, the influence of normal force, displacement and sliding distance differs between the various temperature sections and the related tribological mechanisms.

In this study, premature damage in cylindrical roller bearings made of 100Cr6 (SAE 52100) was investigated. For this purpose, full bearing tests were carried out using two different lubricant formulations with similar viscosities. Published research has pointed out the occurrence of tribo-chemical reactions that cause lubricant degradation and the release of hydrogen in tribo-contact. Hydrogen content measurements were conducted on tested samples, and these measurements showed dependence on the lubricant formulations. Hydrogen diffusion and trapping were identified as significant factors influencing premature damage. The measurement of trapping energies was conducted by thermal desorption spectroscopy, whereas residual stresses, which influence hydrogen diffusion and accumulation, were measured using X-ray diffraction. The measured trapping energies indicated that rolling contact caused the creation and release of hydrogen traps. Over-rolling resulted in changes in residual stress profiles in the materials, demonstrated by changes in stress gradients. These can be directly linked to subsurface hydrogen accumulation. Hence, it was possible to determine that the location of the microstructural damage (WEC) was correlated with the residual stress profiles and the subsurface von Mises stress peaks.

Extremely reliable and wear-resistant components are required for subsea pump applications. For this purpose, materials and components were developed and qualified within the framework of a joint project1, which under media lubrication with water containing particles, exhibit the highest possible wear resistance and can thus achieve the longest possible service life. The developed SiC-bonded diamond ceramics have diamond contents of up to 60 % by volume and can be manufactured in the form of a solid material or as graded components containing diamonds only in the tribologically stressed areas. The results show that the investigated diamond-containing ceramics are very suitable for media-lubricated sliding bearings and mechanical seals in subsea applications. The friction values under media lubrication are very stable and independent of tribological loads. In mechanical seal application, SiC-bonded diamond shows significantly better friction performance than the reference material SiC. An outlook is given on demonstrator tests that are currently in preparation.

When finger joints become immobile due to an accident during sports or a widespread disease such as rheumatoid arthritis, customised finger joint implants are to be created. In an automated process chain, implants will be produced from ceramic or metallic materials. Artificial intelligence-supported software is used to calculate three-dimensional models of the finger bones from two-dimensional X-ray images. Then, the individual implant design is derived from the finger model and 3D printed. The 3D printing process and the structures used are evaluated via model tests and the final implant design via a reliability calculation in a way to ensure that this is also possible via an AI process in the future. Using additive manufacturing with silicon nitride-based ceramics, model specimens and implants are produced via the lithography-based ceramic vat photopolymerisation process with full geometry or elements of triple periodic minimal surfaces structure. The model specimens are tested experimentally, and the loads are matched with a characteristic strength assuming a Weibull distribution of defects in the volume to generate and match failure probabilities. Calculated fracture forces of the silicon nitride-based ceramic structure was validated by comparison of simulation and tests, and the calculation can be used as a quality index for training of artificial intelligence in the future. The proposed method for individualized finger implant design and manufacturing may allow for correction of potential malpositions of the fingers in the future.

The aim of this study is to investigate the atmospheric effect on the wear of cast iron against chromium plated steel at temperatures up to 800 degrees C. Reciprocating wear tests of a cylinder-on-plate configuration were performed in air and a low-oxygen CO2-N2-O2 atmosphere and analyzed.At low temperatures an adhesive wear regime with material transfer from the cast iron cylinder onto the chromium plating was observed up to 400 degrees C. Higher temperatures lead to a tribologically generated oxide layer at the interface, a so-called "glaze layer", resulting in a strong wear decrease. The micro structural analysis reveals a layered structure of differently strong compacted wear particles consisting mainly of iron oxide Fe2O3.A modification of the surrounding atmosphere to an oxygen amount of 5 vol% showed little impact on this tribological behavior above the threshold temperature of 400 degrees C. Sufficient oxidation times of the generated wear particles were assumed, which is a necessary step of the layer formation. Based on this finding, a temperature related sintering or phase transition process is postulated to explain the glaze layer formation independently of the surrounding, oxygen containing atmosphere.Nevertheless, for the adhesion dominated regime at temperatures below 400 degrees C, a positive influence on the wear behavior in the CO2-N2-O2 atmosphere was observed. This change in the tribological behavior is attributed to a carbon enriched layer of 400 nm thickness, which is formed by comparatively less oxidized spheroidal graphite of the cast iron.

In this work, self-lubricating and electrically conductive polymers on a polypropylene (PP) matrix were prepared and investigated. These properties were obtained by additivating PP with carbon black (CB) and multi-walled carbon nanotubes (MWCNTs), in combination with a surface active ionic liquid (IL, trihexyltetradecylphosphonium docusate [P66614][DOC]). These polymeric composites are expected to achieve coefficients of friction (COFs) comparable to lubricated systems. Combined with electrical conductivity, these materials could be applied in electrically loaded tribosystems. The COF was reduced by up to 25% compared to that of plain PP, and high electrical conductivity and self-lubrication were achieved. Fundamental differences between the carbon-based fillers in their interaction with IL were investigated with high-resolution surface analysis (TEM, AFM) and Raman and ATR-FTIR spectroscopy. By varying the tribological test parameters, the application limits of self-lubrication were identified. It was demonstrated that the contact pressure has a strong influence on the COF. Therefore, this work points to potential applications in (e.g. 3D-printed) bearings and electrically loaded bearings where electrical conductivity and relatively low COFs are required.

Non-mechanical stimuli are used to directly control or program the friction properties of tribosystems. For this purpose, an ionic liquid is used as a lubricant that affects and controls the friction in the presence of external triggers. Here, it is shown that the friction behavior of two surfaces in sliding contact can be controlled and permanently changed by applying an electrical potential to an ionic liquid mixture (ILM). This change in the friction properties was demonstrated both at the nanoscale using an atomic force microscopy (AFM)-based friction force microscopy (FFM) and at the macroscale using a specially designed tribo-setup cell. In tribology, the linking of these two scales of magnitude represents one of the greatest obstacles between basic research and the step towards application-oriented system development and is therefore of fundamental importance. In addition, other parameters affecting the tribological behavior of the system, such as roughness, lubricant film thickness, and wear behavior, were investigated as a function of the electrical potentials. The correlation between the structure of surface-bound ionic liquid layers and the friction behavior can be used to control friction, thus enabling a first step towards tribosystems that automatically adapt to changing conditions.

Objective: This interlaboratory round robin test investigated the robustness of the ChevronNotch Beam (CNB) test method and the effect of the processing and testing variations on the fracture toughness of a dental 3Y-TZP ceramic. Methods: The round robin test was performed precisely following the procedures re-commended in ISO 24370:2005 and applied on a commercial 3Y-TZP ceramic (product information). A total of 335 test specimens with dimensions 3x4 x 45 mm(3) was equally distributed among 10 participating laboratories of varying experience in fracture toughness testing. A standard operating procedure was defined with either narrow processing tolerances or alternative (wider) processing tolerances (as proposed in ISO 24370). Fracture toughness data (series 2) was analyzed using one way ANOVA followed by post hoc Tukey HSD test and 95% Confidence Intervals (CI) were computed (p < 0.05). A further, preceding round-robin (series 1) test was conducted with - more possible variations of test conditions regarding CNB notch processing and storage conditions. Those results are summarized in the supplement and discussed with the actual ISO 24370 test. Results: Fracture toughness of the 3Y-TZP ceramic material, summarized over all laboratories was measured to K-Ic = 4.48 +/- 0.11 MPam(0.5) for the standard processing tolerance and K-Ic = 4.55 +/- 0.31 MPam0.5 for the alternative tolerance. The results revealed a significant influence of cutting offset and notch geometry on K-Ic when using CNB method. The test medium also has a significant influence on K-Ic in terms of reduced fracture toughness under the influence of water. With defined testing conditions the number of valid tests and reduced standard deviation increased. In case of strictly following such standard operation procedures, K-Ic can be determined with high reliability. There is no difference between the involved laboratories, but significant influence of cutting offset on K-IC was observed. Significance: The CNB method is suitable method for determination of KIc on fine-grained ceramics such as 3Y-TZP ceramic. By using tighter tolerances for processing and testing, i.e. closely following the ISO 24370 procedure, a highly-precise evaluation of fracture toughness with low data variation is achievable. The information of the storage medium should always be reported along with the data. CNB fracture toughness testing is an alternative method compared to Single-edge V-notch beam (SEVNB), especially for fine-grained ceramics. (C) 2022 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

Two different types of graphene materials were used as functional nanofillers for the mechanical and tribological improvement of silicon carbide/graphene nanocomposites. On the one hand is thermally reduced graphite oxide (TRGO) reduced at three different temperatures, and on the other hand is graphene made of three different organic precursors, which were directly coated on silicon carbide (SiC) platelets (GSiC). Additionally, benchmark materials were also used as carbon fillers. The SiC/graphene nanocomposites with 2 wt% filler content were manufactured by pressureless sintering (PLS). Some composites were produced with higher graphene contents of 4% and 8% and sintered by spark plasma sintering (SPS). Microstructural analyses were conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Underwater lubrication, the SP sintered TRGO and GSiC materials with high graphene content have shown the most promising tribological performance. Furthermore, the reduced size of the homogeneously distributed nanoparticles promotes the formation of surface states, which improve the friction and wear properties.

The aim of the work is to improve tribological properties of an ATF oil by means of additives. Two ionic liquids (IL) and one IL with 0.1 wt.% graphene were chosen as candidates. The ILs were selected because of their promising surface interactions and proven synergy with anti‐wear additives. However, little is known about the addition of ILs to fully formulated lubricants, especially in the low temperature range. Therefore, static and sliding friction as well as wear were measured in an application‐relevant temperature range of −30 to 100°C using a rotating ball‐on‐3‐plate test. The best additive for ATF oil for material pairing 100Cr6/polyether ether ketone was 5 wt.% [P66614][TMPP][G] (halogen‐free) and for 100Cr6/sintered iron 3 wt.% [P66614][BTA]. The additives lead to a wear reduction of more than 50%. Furthermore, it could be observed that the selected ILs have different effects on the friction behaviour at the temperatures investigated.

Alumina-based ceramic tools have been successfully applied in high-speed turning of superalloys. In this study, the tribological characteristics of a novel Al2O3-SiCw-TiCn ceramic composite were investigated in unlubricated sliding contact against laser-heated (600 degrees C) and unheated Inconel 718 between 2.5 m/s and 10 m/s. The tribological behavior of the Al2O3-SiCw-TiCn ceramic was compared to a commercial Al2O3-SiCw ceramic. The results indicated similar coefficients of friction (COF) in laser-heated and unheated tests. Below 7.5 m/s, the wear mechanisms in laser-heated tests were brittle fracture, plastic flow and adhesive wear and predominantly brittle fracture in unheated tests. A tribochemical layer mainly containing chromium and oxygen has formed on the contact surface at 10 m/s resulting in lowering the COF and reducing wear.

Zusammenfassung Durch Reibung und Verschleiß werden weltweit Gesamtkosten von 250 Mrd. €/Jahr verursacht und 8120 MtCO 2 -Emissionen freigesetzt. Die aktuellen Herausforderungen bestehen darin, die Vorteile ultraniedriger Reibung, der verschleißlosen Gleit- und Reibungskontrolle sowie der wasserbasierten Schmierung hinsichtlich Energie- und Ressourceneffizienz für technische Anwendungen zu nutzen. An dieser Problematik, der Steigerung der Energieeffizienz und Nachhaltigkeit, setzt diese Arbeit an. Vorarbeiten haben gezeigt, dass mit speziellen mesogenen Flüssigkeiten Superlubrizität (µ < 0,005) realisiert werden kann. In dieser Arbeit sollen neben der anwendungsnahen Prüfung dieser mesogenen Fluide auch die Eigenschaften von Wasser als Schmierstoff durch Additivierung mit komplexen Fluiden (ionischen Flüssigkeiten, lyotroper Flüssigkristall) und Einbringung eines elektrochemischen Schutzes durch galvanische Kopplung verbessert werden. Durch die Zugabe der komplexen Fluide in Wasser wurden Reibung- und Verschleiß in Modellreibversuchen verbessert. Gleitlagerversuche mit dem mesogenen Schmierstoff zeigen bei galvanisch induziertem Oberflächenpotenzial, durch Kopplung des Stahllagers mit Kupfer, eine Reibwertreduzierung um 60 % und eine Verschleißreduktion um 40 % im Vergleich zu einem Referenzöl.

Under extreme working conditions such as high temperature, strong electric and magnetic fields and acidic or basic environments, ceramic springs offer a clear advantage over conventional steel springs. In this study, a tailored grade of silicon nitride ceramic was characterized as spring material. The basic characterization was complemented with component tests. Bend bars, helical springs and conical disk springs were manufactured and tested under various loading scenarios. Manifested by the smallest effective volume of the three tested geometries, helical springs showed the highest fatigue strength. Nevertheless, the complexity involved in manufacturing helical springs pertaining to their geometrical features resulted in a relatively large scatter in fatigue data. The results pointed out the importance of proper design and machining of the contact surface edges in disk springs, which bear the highest stresses. This work demonstrates the potential of producing ceramic springs with broad applicability and sufficient strength and fatigue resistance.

Water-based lubricants might become an interesting alternative to conventional oil-based lubricants and help to reduce wear as well as improve the energy efficiency of transport processes. Since pure water is generally a rather poor lubricant due to its low viscosity and corrosiveness, it must be tribologically optimized with suitable additives. Here, we study the friction behavior of alkyl glucopyranosides (AGPs) with varying lengths of the alkyl chain. Sliding experiments show that a significant reduction in the coefficient of friction compared to that of pure water is observed. The extent of friction reduction depends strongly on the concentration and on the shearing conditions. It is assumed that the low coefficients of friction are due to the ability of AGPs to form liquid crystalline phases with an ordered structure in the friction gap. Furthermore, the interaction of the AGPs with the surface forms a wear protection layer (boundary lubrication). The friction properties of the water-based system are compared to those of a conventional, mineral oil-based lubricant.

In this study, the decomposition of a multialkylated cyclopentane (MAC) and a perfluoro-poly-ether (PFPE) lubricant was investigated in a ball-on-disc sliding test under vacuum and in a rolling contact fatigue (RCF) test on full bearings. In situ mass spectrometry was conducted to study the tribochemical formation of hydrogen in a steel-on-steel ball-on-disc sliding contact. Further investigations on lubricant degradation in rolling-sliding contact indicated fragmentation and oxidation reaction of the MAC oil by interaction with the oxide layer and the nascent bearing steel.Finite element method (FEM) analysis was carried out to model the contact in the ball-on-disc experiments and to extract contact surface temperature fields. Post-RCF hydrogen analysis of bearing components indicated increased hydrogen content in the samples lubricated with the MAC fluid. The RCF tests with PFPE did not indicate any signs of surface damage.